U.S. patent application number 12/026792 was filed with the patent office on 2008-06-19 for cable length sensor.
This patent application is currently assigned to Micro-Epsilon Messtechik GmbH & Co. KG. Invention is credited to THOMAS BIRCHINGER, JAROSLAV HRUBY.
Application Number | 20080141548 12/026792 |
Document ID | / |
Family ID | 38157912 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080141548 |
Kind Code |
A1 |
BIRCHINGER; THOMAS ; et
al. |
June 19, 2008 |
CABLE LENGTH SENSOR
Abstract
A cable length sensor, in particular, a bowden cable
displacement sensor, comprising a cable drum, a measuring cable
wound on the cable drum and a return device at least lightly
pre-tensioned in the start position, wherein the measuring cable
may be withdrawn by rotating the cable drum against the force of
the return device and by withdrawing the measuring cable the return
device may be further tensioned. The return device is arranged in a
housing, and coupling means for releasably coupling the return
device to the rotating movement of the cable drum are provided so
as to permit ready removal and replacement of the return device.
Also, the housing may be provided with a sensor element operated
from outside the housing for determining the current position of
the return device, in particular the at least lightly tensioned
starting position of the return device.
Inventors: |
BIRCHINGER; THOMAS;
(Furstenzell, DE) ; HRUBY; JAROSLAV; (Bechyne,
CZ) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA, 101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
Micro-Epsilon Messtechik GmbH &
Co. KG
|
Family ID: |
38157912 |
Appl. No.: |
12/026792 |
Filed: |
February 6, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/DE2007/000347 |
Feb 23, 2007 |
|
|
|
12026792 |
|
|
|
|
Current U.S.
Class: |
33/734 |
Current CPC
Class: |
B66D 5/32 20130101; G01B
3/11 20130101 |
Class at
Publication: |
33/734 |
International
Class: |
G01B 3/11 20060101
G01B003/11 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2006 |
DE |
10 2006 008 947.2 |
Feb 7, 2007 |
DE |
10 2007 006 813.3 |
Claims
1. A cable length sensor, said sensor comprising: a cable drum, a
measuring cable wound on the cable drum, and a return device which
is pre-tensioned at least slightly in a starting position, the
measuring cable configured to be drawn off the cable drum against
the force of the return device by turning said cable drum, and the
return device further configured to be tensioned by drawing off the
measuring cable, wherein the return device is disposed in a
housing, wherein a coupling means for coupling the return device to
the direction of turning of the cable drum is provided, and wherein
a fixing means, which can be actuated from outside of the housing
and which serve for fixing the current position of the return
device, is associated with the housing.
2. The Cable length sensor according to claim 1, wherein the return
device comprises an axle rotatably mounted in the housing, and one
or more return elements which can be tensioned individually or
together, and in a starting position are pre-tensioned between the
housing and one of the axle or the coupling means.
3. The Cable length sensor according to claim 2, wherein the return
elements are implemented as springs.
4. The cable length sensor according to claim 3, wherein the
springs are flat spiral springs.
5. The cable length sensor according to claim 3, wherein the
springs work together with the coupling means via the axle.
6. The cable length sensor according to claim 5, wherein the axle
extends, at least slightly, out of the housing.
7. The cable length sensor according to claim 5, wherein the
coupling means acts between the axle of the return device and an
axle of the cable drum.
8. The cable length sensor according to claim 7, wherein the
coupling means serves to releasably connect the two axles in such a
manner that they are fixed with respect to turning.
9. The cable length sensor according to one of the claim 2, wherein
the return elements are disposed in a first housing section and the
coupling means is disposed in a second housing section.
10. The cable length sensor according to one of the claim 10,
wherein the second housing section is open on a side facing away
from the first housing section.
11. The cable length sensor according to claim 9, wherein the first
housing section together with the second housing section forms
spring box.
12. The cable length sensor arrangement according to claim 9,
wherein the fixing means is associated with the second housing
section.
13. The cable length sensor according to claim 9, wherein the
fixing means acts from outside of the housing on at least one of
the axle of the return device or the coupling means.
14. The cable length sensor according to claim 12, wherein the
fixing means comprises at least one arresting pin which extends
through the housing wall to one of the axle of the return device or
the coupling means.
15. The cable length sensor according to claim 1, wherein the cable
drum is disposed in a housing on which the housing of the return
device is flange-mounted.
16. The cable length sensor according to claim 15, wherein an
additional fixing means is associated with the housing of the cable
drum, said additional fixing means serving to arrest the cable drum
in such a manner that it is fixed with respect to turning.
17. The cable length sensor according to claim 16, wherein the
additional fixing means comprises an arresting pin which extends
through the housing of the cable drum.
18. The cable length sensor according to claim 17, wherein the
arresting pin engages in a position on an end face of the cable
drum when in its position arresting the cable drum.
19. The cable length sensor according to claim 15, wherein the
housing of the cable drum has a greater diameter than the housing
of the return device.
20. The cable length sensor according to claim 17, wherein the
housing of the cable drum projects radially beyond the housing of
the return device, and wherein the arresting pin projects into the
housing of the cable drum via the end wall of the housing of the
cable drum at a location which projects beyond the housing of the
return device.
21. The cable length sensor according to claim 1, further
comprising a sensor element for detecting turning of the cable
drum.
22. The cable length sensor according to claim 21, wherein the
sensor element is associated with a turning axle of the cable drum
or a turning axle of the return device.
23. The cable length sensor according to claim 21, wherein the
sensor element is flange-mounted on a side of the cable drum and is
connected in such a manner that it is fixed with respect to
turning, to an axle of the cable drum.
24. The cable length sensor according to claim 23, wherein the
sensor element is flange-mounted on that side of the housing of the
cable drum facing away from the return device.
25. The cable length sensor according to claim 23, wherein the
sensor element is flange-mounted on the housing of the cable drum
via a housing bracket.
26. The cable length sensor according to claim 25, wherein the
sensor element is a rotary sensor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Continuation of International
Application No. PCT/DE2007/000347, filed Feb. 23, 2007, and which
designates the U.S. The disclosure of the referenced application is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a cable length sensor, in
particular to a Bowden cable displacement sensor, with a cable
drum, a measuring cable wound on the cable drum, and a return
device which is pre-tensioned at least slightly in the starting
position, where the measuring cable can be drawn off the cable
drum, against the force of the return device, by turning said cable
drum and where the return device is further tensioned by drawing
off the measuring cable.
BACKGROUND OF THE INVENTION
[0003] At this point let it be noted that the discussion here is in
fact of a cable length sensor and accordingly of a cable drum and a
measuring cable but, however, the term "measuring cable" is to be
understood in the sense of "means for measurement". When using a
measuring cable it can be of any material, e.g. of metal or metal
alloys, of single-conductor metal, or of textile of the most varied
type of manufacture. Instead of using a measuring cable, using a
measuring band is possible, where said band can also be made of
textile material, of plastic, or of metal. Finally, it is essential
that the medium serving for the measurement is made so as to be
stable longitudinally or with respect to drawing. What the means
are in a concrete case is not essential for the teaching
claimed.
[0004] Cable length sensors of the generic type have been known for
years in the most varied embodiments. Among the essential
components of such a cable length sensor is the measuring cable
which is fastened on its end side to the object to be detected in
its current position. The measuring cable is wound on the cable
drum and is pre-tensioned by the return element. Depending on the
application in question, a respective sensor can be provided, which
is coupled to the cable drum. Since the diameter of the cable drum
is known, the cable length drawn off can be determined via the
sensor via an evaluation unit, which is usually external.
[0005] In the known cable length sensor the measuring cable is
wound onto the cable drum, where the return element is
pre-tensioned at least slightly in the completely wound-on state of
the cable drum. If the object and the sensor move relative to one
another, the measuring cable is drawn from the cable drum. In the
reverse direction of motion, therefore when the measuring cable is
once again wound onto the cable drum due to the return force of the
return element, a motion of the object towards the cable drum or
towards the sensor element occurs.
[0006] As published state of the art let us name, merely by way of
example, EP 0 778 239 B1, which shows a generic cable length
sensor. Furthermore, let us refer to US 443,888, which also shows a
generic cable length sensor. In both cases the cable drum and the
return device are disposed in a housing, where, for replacing the
return device, it is necessary to replace the entire cable length
sensor and to dismount it--at the factory.
[0007] In regard to the state of the art known from practice let it
be pointed out that the cable length sensors of the generic type
frequently use wire potentiometers or hybrid potentiometers as
sensor elements. A significant disadvantage in the case of these
sensor elements is their short service lifetime, which in this
respect defines the service lifetime of the entire cable length
sensor. For this reason, conductive plastic potentiometers or
wear-free inductive, magnetic, or optical sensors, among others,
have been used in the meantime, since their service lifetime is
significantly longer. In such a case the service lifetime of the
cable length sensor is not limited by its respective sensor element
but rather routinely by the service lifetime of its return device.
Typical service lifetimes for commercially available return devices
are in the range from 1 to 2 million cycles, where one cycle
corresponds to one complete winding off and one complete winding on
of the measuring cable. With unfavorable conditions of use, e.g. at
high cable speeds and/or accelerations of the measuring cable, the
service lifetime of the cable length sensor can be clearly
reduced.
[0008] If the cable length sensor is used with very frequent
motion, an extremely low short service lifetime is to be expected,
since, specifically, damage occurs very frequently, even after a
few months. This situation is customarily countered either by a
damage-related replacement of the sensor or by a preventive
replacement of the sensor in the framework of a relatively short
service interval. Instead of replacing the entire cable length
sensor, it is also conceivable to replace merely the spring
elements of the return device, which, however, entails a
significant effort.
[0009] It is to be noted that a break in a spring in the return
device routinely leads to additional damage, e.g. to a tear in the
measuring cable. In such a case it is necessary to dismount the
complete cable length sensor and to mount a replacement device.
Dismounting and mounting on site by unqualified personnel is
practically not possible so that a special repair service is
necessary. Among the significant disadvantages are, in particular,
also long machine downtimes, since specifically the complete cable
length sensor must be removed and a new cable length sensor must be
installed, where, due to storing a complete cable length sensor in
advance, high storage costs arise.
[0010] Furthermore, it is necessary in the case of a complete
replacement of the cable length sensor to calibrate the control
and/or the entire cable length sensor. The defective cable length
sensor is customarily sent to the manufacturer, which entails a
significant administrative overhead as well as transport costs.
Since the conventional repair of the cable length sensor is very
labor-intensive, relatively high repair costs arise. Additional
costs are to be expected in case of consequential damage to the
cable length sensor.
[0011] If one wishes to prevent an instance of damage, preventive
replacement within a service interval presents itself in the case
of conventional cable length sensors. In this case the sensor is to
be replaced, more or less regularly, or the cable length sensor in
use is to be removed each time. A new cable length sensor, always
to be stored in advance, is to be installed by skilled personnel,
which in accordance with the discussions above, entails significant
storage costs for storing a cable length sensor in advance.
[0012] After the installation of the new cable length sensor, the
control and/or the complete cable length sensor must be
recalibrated. The replaced cable length sensor is sent to the
manufacturer, due to which, however, costs arise, namely, on the
one hand, costs due to administration and, on the other hand, costs
due to transport. The cable length sensor sent to the manufacturer
is generally overhauled, which, once again, is labor-intensive.
[0013] If one takes into consideration the fact that the return
device's springs or spring packs previously indicated as a weak
point are replaced separately, then this could theoretically be
done on site or at the manufacturer's. In the case of prior-art
cable length sensors, thus, for example, according to EP 0 778 239
B1 or US 443,888, the spring replacement alone represents an
extremely labor-intensive process. Furthermore, highly qualified
technical personnel are necessary, which, in particular, have at
their disposal the special tools needed in each case. Moreover, for
numerous forms of construction there is a quite significant danger
of injury due to a spring possibly jumping out of the housing as
soon as the housing is opened and the spring of the return device
are withdrawn.
[0014] The work to be carried out in replacing the spring of the
return device is particularly complex, in particular when the cable
length sensor has several springs disposed in series or in
parallel. To replace the springs the complete housing, or at least
the spring box, must be opened. The springs must be de-tensioned,
where a pre-tensioning of typical spring packs can be up to 30
revolutions. If the springs, after the de-tensioning, are replaced,
care must be taken that they are connected to one another and/or to
the turning axle. If new springs or spring packs are introduced,
they must be compressed to generate tension. This is probably the
most laborious step of the operation since up to 150 spring
revolutions are necessary for this. It is not possible to compress
the springs without a special tool. Moreover, there is the danger
that in compressing the springs, errors are made in the permissible
number of revolutions, which in turn reduces the service lifetime
of the spring or the spring pack. Furthermore, it is
disadvantageous that the work necessary to replace the individual
springs is, as a rule, only possible when the complete cable length
sensor has been dismounted from the respective system. This also
requires a quite significant investment of time and ultimately
causes downtime of the respective machine, system, and so on.
[0015] In light of the explanations above, the present invention is
based on the objective of developing and extending the cable length
sensor of the generic type so that maintenance and repair of the
complete cable length sensor is possible with as little effort as
possible, even by less qualified personnel.
SUMMARY OF THE INVENTION
[0016] The objective above and others are realized by a cable
length sensor with the features of the claimed invention. Such a
cable length sensor is characterized by the fact that the return
device is disposed in a housing, that a coupling means for coupling
the return device to the direction of turning of the cable drum is
provided, and that a fixing means, which can be actuated from
outside of the housing and which serves for fixing the current
position of the return device, in particular the at least slightly
pre-tensioned starting position of the return device, is associated
with, or can be associated with, the housing.
[0017] It has been recognized according to the invention that in
the generic cable length sensor the return device is a weak point
with respect to service lifetime or with respect to maintenance
and/or repair. The set of problems related to this can be avoided
in an additional manner according to the invention by the fact that
the complete return device is disposed in its own housing, where a
coupling means for coupling the return device to the direction of
turning of the cable drum is provided. Furthermore, a fixing means,
which can be actuated from outside of the housing and serve for
fixing the current position of the return device, in particular the
at least slightly pre-tensioned starting position of the return
device, is associated with, or can be associated with, the
housing.
[0018] The core concept of the present invention accordingly lies
in a quite particular modular construction of the cable length
sensor, namely to the effect that the complete return device can be
replaced in an already pre-tensioned, i.e. usable, condition. For
this the return device is designed to have modular form.
Accordingly the return device is already compressed in the housing
so that dismounting as well as mounting of the complete return
device, in functional condition, is possible. Accordingly, the
return device is shipped, and in given cases stored, in the
pre-tensioned state.
[0019] In an advantageous manner the return device comprises at
least one return element, where in a still more advantageous manner
it is possible to dispose two, three, or more return elements in
parallel to one another or in series with one another. In the
starting position the return elements are pre-tensioned between the
housing and an axle or the coupling means.
[0020] In particular in the framework of a particularly simple
development, the return elements are implemented as springs, where
spiral springs are particularly well-suited due to their
approximately rotationally symmetric structure. When using flat
spiral springs the idea presents itself of arranging them
concentrically about the turnable axle of the return device, where
the inner end of the flat spiral spring is connected to the axle
and the outer end of the flat spiral spring is connected to the
housing or to retaining elements carried by the housing so that a
pre-tensioning can be developed in accordance with the
arrangement.
[0021] As has already been explained previously, the springs work
together with the coupling means via an axle, preferably running in
the center. The axle can extend, at least slightly, out of the
housing, but this is not absolutely required.
[0022] Also, it is conceivable that the axle is a type of hollow
shaft in which a coupling is housed. Into it a solid shaft with
corresponding coupling element could be inserted. When using such a
hollow shaft it would not have to project out of the housing.
[0023] In particular when using an axle extending at least slightly
out of the housing, the coupling means acts between the axle of the
return device and an axle of the cable drum in order specifically
to connect the two axles to one another in a such manner that they
are fixed with respect to turning. In the framework of a quite
particularly simple coupling the two axles are aligned to one
another.
[0024] In concrete terms, it is conceivable that the return
elements are disposed in a first housing section and the coupling
means in a second housing section, preferably open on the side
facing away from the first housing section. The second housing
section, open on one side, serves to connect to the housing of the
cable drum or flange-mounting on it. Accordingly, the axle of the
cable drum should project out of the housing of the cable drum so
that the two axles can be connected to one another, at their end
sides, within the second housing section and via the coupling
means.
[0025] The first housing section of the return elements customarily
formed as springs comprises, formed in given cases together with
the second housing section, a type of spring box, which is
implemented as a modular component, and to that extent a
replaceable one.
[0026] According to the explanations above, the return device can
be held by means of the fixing means in the at least slightly
pre-tensioned starting position. The fixing means is essentially
associated with the second housing section. They act, from outside
of the housing, on the axle of the return device and/or on the
coupling means so that, on activation of the fixing means, turning
of the axle caused by the force of the springs is effectively
avoided. With activated fixing means the tension between the
housing and the axle can be maintained with interconnection of the
springs so that the return device formed with a modular design can
be handled independently of the other components of the cable
length sensor.
[0027] In concrete terms, it is advantageous if the fixing means
comprises at least one arresting pin which extends through the
housing wall to the axle of the return device or to the coupling
means. In so doing, it is conceivable that the arresting pin is
provided at least in some areas with an outer thread so that it can
be screwed either into the housing wall or into the axle or into
the coupling means. A simple plugging in using a certain clamping
action is also conceivable.
[0028] As has already been mentioned previously, the cable drum is
also disposed in a housing, where the return device can be
flange-mounted on the housing of the cable drum, preferably via the
second housing section.
[0029] A fixing means is also associated with, or can be associated
with, the housing of the cable drum, said fixing means serving to
arrest the cable drum in such a manner that it is fixed with
respect to turning. For the purpose of dismounting or mounting, the
cable drum can thus be arrested within its housing in order
specifically to enable or aid the flange-mounting of the return
device. In concrete terms, the fixing means of the cable drum
comprises at least one arresting pin extending from outside of the
housing through it up to the cable drum, said arresting pin
exerting a clamping action on the cable drum. Also, it is
conceivable that the arresting pin engages in a corresponding
recess on or in the cable drum, where the arresting pin acts in a
quite particularly advantageous manner in its arresting position on
an end face of the cable drum.
[0030] With regard to simple handling of the cable length sensor
for the purpose of replacing the return device it is furthermore
advantageous if the housing of the cable drum has a greater
diameter than the housing of the return device. In the framework of
such a development it is possible that the arresting pin of the
cable drum projects into it via an end wall of the housing of the
cable drum, specifically that end wall that projects above the
housing of the return device, so that handling of the arresting pin
for blocking the cable drum is possible from outside and in fact
even in the case of a flange-mounted return device. Thereby the
mounting or dismounting of the return device is aided quite
significantly.
[0031] In a still more advantageous manner a sensor element for
detecting turning of the cable drum is provided, above all when the
cable length sensor is a type of Bowden cable displacement system.
The sensor element serves for detecting turning of the cable drum,
where in the case of known drum diameters the cable length wound on
or drawn off can be determined exactly.
[0032] The sensor element can be associated with the turning axle
of the cable drum or the turning axle of the return device. Thus,
in any case a bilateral application of the sensor element is
conceivable when the turning axles project outwards on both sides
of the respective housing so that a mechanical coupling of the
sensor elements is possible.
[0033] In a particularly advantageous manner the sensor element is
flange-mounted on a side of the cable drum, specifically that side
facing away from the return device, preferably on its housing, and
along with this is connected, in such a manner that it is fixed
with respect to turning, to the turning axle of the cable drum. For
this a special housing bracket can be provided which in turn is
flange-mounted on the housing of the cable drum. The sensor element
connects, as a modular component, directly to this housing bracket
so that, in the simplest manner, it can also be removed, as such,
from the housing of the cable drum, or from the housing bracket
provided there. A connection, fixed with respect to turning,
between corresponding coupling means on the sensor element and on
the free end of the turning axle of the cable drum can be
realized.
[0034] Furthermore, let it be noted that the sensor element can be
any sensor, preferably a rotary sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The inventive device will be described in more detail
hereinbelow with the aid of an exemplary embodiment of the
inventive apparatus, with reference to the accompanying
drawings.
[0036] FIG. 1 shows in an exploded schematic view, an embodiment
example of a cable length sensor according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0037] FIG. 1 shows an exemplary embodiment of a cable length
sensor according to the invention with its essential components.
The cable length sensor shown here is a concrete example of a
Bowden cable displacement sensor. It comprises a cable drum 1 and a
measuring cable 2 wound on the cable drum 1, where the measuring
cable 2 is only indicated at the measuring cable output 3.
[0038] The cable length sensor furthermore comprises a return
device 4 which is at least slightly pre-tensioned in the starting
position, where the measuring cable 2 can be drawn off the cable
drum 1, against the force of the return device 4, by turning said
cable drum and where the return device 4 is further tensioned by
drawing off the measuring cable 2.
[0039] According to the invention the return device 4 is disposed
in a housing 5. Furthermore, a coupling means 6 is provided which
serves to couple the return device 4 to the turning motion of the
cable drum 1. A fixing means 7 serves to fix the current position
of the return device 4, in particular the at least slightly
pre-tensioned starting position of the return device 4. The fixing
means 7 is associated with, or can be associated with, the return
device.
[0040] The single FIGURE allows one to see that the return device 4
comprises three return elements acting in parallel, where each of
the return elements is implemented as a spring 8. Each spring 8 is
arrested at its inner end with a turnable axle 9 and at its outer
end on the housing 5 or on corresponding retaining pins which in
turn are fastened on the housing 5. Consequently, the springs 8 can
be tensioned between the housing 5 and the axle 9, where the
tensioning and detensioning are done via a turning of the axle
9.
[0041] The axle 9 running in the center of the housing 5 extends,
at least slightly, out of the housing 5 and works together there
with the coupling means 6. In concrete terms, the coupling means 6
acts between the axle 9 of the return device 4 and an axle 10 of
the cable drum 1.
[0042] The coupling means 6 serves for connecting, in a manner
fixed with respect to turning, the aligned axles 9 and 10, where
the coupling means 6 can comprise several components.
[0043] The single FIGURE furthermore allows one to see that the
return elements or springs 8 of the return device 4 are disposed in
a first housing section 11 in a nearly enclosed manner. The
coupling means 6 is disposed in a second housing section 12 open on
the side facing away from the first housing section 11.
[0044] Together, the two housing sections 11 and 12 form a type of
spring box, where the second housing section 12 serves for
flange-mounting on the housing 13 of the cable drum 1.
[0045] The fixing means 7 is furthermore associated essentially
with the second housing section 12, where the fixing means 7 acts,
from outside of the housing 5 or the second housing section 12, on
the axle 9 of the return device 4 or on the coupling means 6
provided there. In concrete terms, the fixing means 7 comprises an
arresting pin 14 which extends through the housing wall to the axle
9 of the return device 4 or to the coupling means 6 provided
there.
[0046] As already mentioned previously, the cable drum 1 is
disposed in the housing 13. The housing 5 of the return device 4,
or the second housing section 12 of the return device 4, can be
flange-mounted on the housing 13.
[0047] The single FIGURE furthermore allows one to see that on the
housing 13 of the cable drum 1 a fixing means 15 is also provided
which serve to arrest, in a manner fixed with respect to turning,
the cable drum 1. The fixing means 15 comprises an arresting pin 16
extending from outside through the housing 13, said arresting pin,
in the simplest case, holding the cable drum 1 in the current
turning position by clamping action.
[0048] Fastening screws 17 serve to secure the two housings 13 and
5 (comprising the housing sections 11 and 12) together.
[0049] On a side of the housing 13 of the cable drum 1,
specifically the side lying opposite the return device 4, a sensor
element 18 is disposed which serves to detect turning of the cable
drum 1. The sensor element 18 is connected via a flange or housing
bracket 19 and in such a manner that it cannot turn, to the axle 10
of the cable drum 1, where the sensor element 18 is also designed
or implemented in a modular form. Also, the sensor element 18 can
be removed from the housing 13 of the cable drum 1, or individual
modules of said sensor element can be replaced, in a simple
manner.
[0050] If, in the cable length sensor according to the invention,
it becomes necessary to replace the return device 4 with the
springs 8 located therein, the cable length sensor is brought into
a position in which the measuring cable 2 is wound completely on
the cable drum 1. Thereafter, the cable drum 1 is locked in its
position, specifically via the fixing means 15 provided for this,
or the arresting pin 16 provided for this. The same applies to the
return device 4 or to the springs 8 located therein. Thus, the
complete spring pack is locked by means of the fixing means 7 or by
means of the arresting pin 14 provided for this. The fastening
screws 17 are loosened so that the entire return device with the
springs 8 located therein can be removed from the housing 13 of the
cable drum 1. A new return device 4, with already pre-tensioned
springs 8 located therein, is plugged on, where between the axle 10
of the cable drum 1 and the axle 9 of the return device 4 a
connection fixed with respect to turning is produced by the
coupling means 6. The fastening screws 17 are tightened.
Subsequently, the arresting pins 14 and 16 are loosened so that the
cable length sensor with pre-tensioned return device 4 can operate.
A replacement of the return device 4 can thus be carried out by
anyone in only a few minutes without a special tool. A new
calibration of the sensor and control is not necessary.
[0051] Finally, let it be noted that the embodiment explained above
serves merely for exemplary discussion of the teaching claimed but
does not restrict it to the disclosed embodiment.
* * * * *